1. Field of the Invention
This invention relates to gauges and, more particularly, to gauges for measuring distortions or irregularities of the shape of cylindrical or truncated cone-shaped objects from desired circular dimensions.
2. Description of the Prior Art
Measuring ovality or the roundness of cylindrical or truncated cone-shaped objects, or distortions or deviations therefrom, is particularly critical in a variety of applications. For example, in the petroleum industry it is extremely important that the threaded connectors between adjacent pipes and other tubular or cylindrical members are formed within established tolerances to provide a secure and tight fit therebetween. Since pipes are often joined together in lengths of many thousand feet and are inserted into deep bore holes in the ground, it is a mandated practice to critically inspect each threaded connector before using a particular pipe. Inspectors scrutinize the threaded connectors for small deviations from accepted norms.
Such standards are set by the American Petroleum Institute and others for equipment used in the petroleum industry. One of the criteria used to judge the perfection or imperfection of threaded connectors is the degree by which the connector deviates from a perfect circle at various locations on the connector. This is important for both straight connectors as well as tapered connectors and is particularly important at the ends where the pipes are threaded together.
Ovality or deviations from perfect roundness of a pipe can occur in a number of different ways. The pipe can be dropped or crushed during shipment or unloading, with resultant damage to its threaded end. The pipe could have been formed out of round before the threads were cut. Finally, damage may occur while the threads were being formed. This is particularly important since a commonly used threading machine grips the pipe at only three places and can cause what is referred to as triangulation errors in the pipe.
A variety of devices are currently used for measuring ovality of the inside or outside surface of a threaded connector. Taper gauges having a two-point contact which spans the diameter of the threaded connector are positioned at a particular location. By moving the gauge plus or minus 90.degree. progressively around the threads, deviations from perfect roundness can be determined by comparing the changes actually measured by the taper gauge with the standards for a perfectly formed pipe. Representative taper gauges are sold by Allen Gauge & Tool Company, the assignee of the present application, under Model Nos. 5606, 5554 and 5572. However, taper gauges cannot readily detect triangulation errors since only two points contact the pipe.
In addition, saddle and C-shaped gauges, such as those sold by Allen Gauge & Tool Company under Model Nos. 5336 and 9800 have been used to measure ovality. See also the gauge shown in U.S. Pat. No. 2,863,223. However, these devices are generally used to measure ovality away from the ends of a pipe. Other devices for measuring ovality are shown in U.S. Pat. Nos. 1,637,482, 2,620,569, 2,770,050, 2,785,474, 3,191,311 3,277,578, and 3,468,034. However, all of these devices have one or more problems which make them unsuitable for field measurements of threaded or unthreaded connectors on petroleum pipe and the like. For example, some of the devices are complicated bench devices or are made specifically for measuring one particular type and size of cylindrical object. In addition, some of these devices are not readily adjustable for varying diameters of pipe and are not particularly suited for field measurements at the end of a pipe with great precision. Moreover, some of these devices are not suitable for measuring the tapered threaded connectors commonly used in the petroleum industry.
Accordingly, it is an object of the present invention to provide an ovality gauge which is portable, hand held, and easily used by an inspector in the field. In addition, it is an object to provide such a device which can be used on tapered, non-tapered, threaded or smooth surfaces. It is an object to provide an ovality gauge which is adjustable for a wide variety of diameters and can provide means for precisely positioning the gauge on the end of an object to measure ovality at a prescribed location. It is also an object to provide a device which can be used to measure the ends of both internal and external surfaces of cylindrical or conical objects.